BlastTalk: Advantages of finer grade garnet (Part II)
In the previous edition, we talked about the advantages of finer versus coarser grade garnet on industrial coatings and explored some practical aspects to consider when choosing the garnet grain size for a desired surface profile. Let’s talk about the different application examples for finer grain garnet.
This process is often used to prepare structures where an existing coating has deteriorated or a recently blasted surface has flash rusted. Intact paintwork needs to be brush blasted to remove loose paint, contamination and produce a surface profile for subsequent recoating.
Any corroded areas will also need to be blast cleaned to a specified standard. A smaller garnet grain abrasive will effectively etch the intact coating, while scouring into any existing surface profile on the exposed substrate, enabling the original profile to be efficiently re-serviced for the new coating. It also facilitates a feathered transition between intact coating and bare steel.
Blasting with a finer grade garnet is beneficial when you have low build coatings or heavily pitted surfaces. Using a finer grade garnet on low build coating systems results in a faster blast with more particles impacting the surface per square foot. In the case of heavily pitted surfaces, finer garnet particles are able to fit into pitted areas to clean where coarser particles cannot.
Therefore, using a finer garnet grade can prevent premature coating failure due to substandard cleanliness. Furthermore, as garnet is an abrasive that generates minimal levels of dust, it facilitates efficient surface preparation without undue contamination of surrounding areas.
In order to achieve a quality and uniform finish, it is essential to use a finer grade garnet to ensure the specified finish is obtained. Often, using a coarser abrasive can result in over-blasting that can produce an unacceptable surface finish. Once that happens, there is no going back.
Aluminium structures and galvanised surfaces
The scouring effect of smaller grains can serve to clean away contamination from surface undulations. Lower air pressure will avoid undue damage to relatively soft surfaces.
In the next edition, we will be talking about advantages on other materials such as fibreglass, graffiti removal, turbines and propellers, when not to use a finer grade garnet and practical considerations.
By John Halewood, Manchester